1. Field of the Invention
The present invention relates to a method and apparatus for lapping or polishing semiconductor silicon single crystal wafer which can produce a wafer having a high degree of flatness in a lapping or polishing step of a semiconductor silicon single crystal wafer, particularly, a large diameter semiconductor silicon single crystal wafer.
2. Description of the Related Art
With a lapping apparatus currently in use for lapping semiconductor silicon single crystal wafers, as workpieces (semiconductor silicon single crystal wafers) have larger diameters, they are generally lapped without reducing the number of workpieces simultaneously loaded or processed in order to pursue higher productivity.
As a result, the lapping apparatus have become larger and heavier, as having a weight of 30-40 tons, so that reconsideration must be taken even for the construction of a building for accommodating the lapping apparatus or the like.
As workpieces of larger diameters are used and apparatus of larger sizes are introduced, a longer time is required for loading and unloading the workpieces for lapping. In view of true working efficiency, the influence of the time required for such operations cannot be ignored.
In considering automated loading operations and so on, difficulties are encountered in loading a plurality of wafers on each of a plurality of carriers, so that a problem arises in bringing the automation into practice.
From a view point of a reduction in weight of apparatus and automation with an introduction of single wafer processing, grinding with a bonded abrasive has been considered as an alternative to lapping but not yet introduced into mass production processes.
The processing of a semiconductor silicon single crystal wafer is basically proceeded in a sequence of slicing, lapping, etching, polishing and cleaning steps.
As workpieces (semiconductor silicon single crystal wafers) have larger diameters, the production scheme has also been changed in form. Specifically, for the slicing, an inner diameter saw has been replaced with a wire saw apparatus.
A wafer cut by a wire saw apparatus, however, exhibits a large deformation called xe2x80x9cundulations (waviness)xe2x80x9d (cross-sectional shape of the wafer) due to the characteristics of the wire saw apparatus, largely affecting the quality of final mirror-polished wafer (sori, bow, flatness and so on).
Generally, for applying the grinding, a vacuum chuck made of ceramics or porous metal, stainless steel or the like is used to chuck a wafer cut by a wire saw apparatus, and the wafer is ground or lapped without a break to a predetermined total grinding or lapping stock removal such as about 50 xcexcm or more for a single side and about 100 xcexcm or more for double sides. However, from the relationship between the hardness of a chucking surface and waviness of the wafer, the transferred waviness remains in the ground or lapped wafer, which is a problem.
The polishing also implies similar problems to those of the lapping as mentioned above. In the polishing, a wafer is polished without a break to a predetermined total polishing stock removal, for example, about 10 xcexcm for a single side and about 20 xcexcm for double sides. Again, the transferred waviness remains in the polished wafer, resulting in a problem as is the case of the lapping.
The present invention has been made in view of the above-mentioned problem inherent to the prior art, and it is an object of the present invention to provide a method and apparatus for lapping or polishing a semiconductor silicon single crystal wafer which can eliminate the transfer of waviness of a wafer cut by a wire saw apparatus, improve the quality of the wafer, realize automated lapping or polishing processes, allow for single wafer processing from a cassette to another cassette, and increase the workability and labor productivity.
To achieve the above object, a method for lapping a semiconductor silicon single crystal wafer according to the present invention is characterized in that a small amount of single-side lapping is repeated alternately on the two surfaces of a semiconductor silicon single crystal wafer to get to a predetermined total lapping stock removal. The stock removal of the small amount of single-side lapping is preferably in a range of 10 to 20 xcexcm.
The lapping method according to the present invention involves chucking a wafer on a vacuum chuck, lapping one surface of the wafer in a range of 10-20 xcexcm, inverting the wafer to lap the other surface thereof in a range of 10-20 xcexcm, and repetitively lapping the two surfaces alternately in a range of 10-20 xcexcm to get to a predetermined total lapping stock removal, for example, 50 xcexcm for one side and 100 xcexcm for double sides.
In the lapping method for the present invention, a small amount of single-side lapping is repeated alternately on the two surfaces of the wafer to get to a predetermined lapping stock removal so that the formation of a reference surface is consequently divided by alternately repeating the single-side lapping. As a result, the transfer of waviness of a wafer caused by a wire saw apparatus, occurring when a predetermined stock removal of lapping is performed without a break, can be alleviated.
A method for polishing a semiconductor silicon single crystal wafer according to the present invention is characterized in that a small amount of single-side polishing is repeated alternately on the two surfaces of a semiconductor silicon single crystal wafer to get to a predetermined polishing stock removal. The stock removal of the small amount of single-side polishing is preferably in a range of 1 to 3 xcexcm.
The polishing method according to the present invention involves holding a wafer on a vacuum chuck, polishing one surface of the wafer in a range of 1-3 xcexcm, inverting the wafer to polish the other surface thereof in a range of 1-3 xcexcm, and repetitively polishing alternately the two surfaces in a range of 1-3 xcexcm to get to a predetermined total polishing stock removal, for example, 10 xcexcm for one side and 20 xcexcm for double sides.
In the polishing method for the present invention, a small amount of single-side polishing is repeated alternately on the two surfaces of a wafer to get to a predetermined total polishing stock removal so that the formation of a reference surface is consequently divided by alternately repeating the single-side polishing. As a result, the transfer of waviness of a wafer caused by a wire saw apparatus, occurring when a predetermined stock removal of polishing is performed without a break, can be alleviated.
An apparatus for lapping or polishing a semiconductor silicon single crystal wafer comprises a wafer chuck for holding a semiconductor silicon single crystal wafer, and a lapping table or a polishing table for lapping or polishing one surface of the semiconductor silicon single crystal wafer held by the wafer chuck.
A wafer inverting device may be provided near the wafer chuck for inverting a semiconductor silicon single crystal wafer, so that the wafer can be readily inverted.
As described above, the present invention can produce effects such as eliminating the transfer of waviness of a wafer cut by a wire saw apparatus, improving the quality of the wafer, realizing automated lapping or polishing, allowing for single wafer processing from a cassette to another cassette, and increasing the workability and labor productivity.